Sigmar Polke (born 1941) recently completed a series of 12 windows for the Grossm?nster cathedral in Z?rich, setting new standards for the mutual relationship between art and church. One group of seven Romanesque windows shows luminous mosaics of thinly sliced agate, some of it artificially colored, to produce pulsating blocks of back-lit color. Says Marina Warner, "The interior of rocks opens not only on unexpected colors... on once imprisoned now...